Heat Transfer Practice Test 4

1. In the non-dimensional Biot number, the characteristics length is the ratio of

Volume of solid to its surface area

Surface area to perimeter of solid

Perimeter to surface area of solid

Surface area to volume of solid

2. What is the absorptivity of the gray body?

Below unity

2.5

Unity

3. Energy strikes a vertical hemispherical plate with an intensity of 640 W/m². The absorptivity is thrice the transmissivity and twice the reflectivity. Determine the rate of transmission

236.74 W/m²

187.87 W/m²

456.09 W/m²

116.37 W/m²

4. Let there is some conduction resistance, then temperature becomes a function of
(i) Biot number
(ii)Fourier number
(iii) Dimensionless parameter

i and ii

ii and iii

i and iii

i, ii and iii

5. Thin glass plate is an example of

Black body

Opaque body

Transparent body

White body

6. The curve for unsteady state cooling or heating of bodies is

Exponential curve asymptotic both to time and temperature axis

Parabolic curve asymptotic to time axis

Exponential curve asymptotic to time axis

Hyperbolic curve asymptotic both to time and temperature axis

7. The temperature perturbation at all the surface has penetrated to the depth

2.6 (α T)^1/2

3.6 (α T)^1/2

4.6 (α T)^½

1.6 (α T)^1/2

8. The total radiant energy A impinging upon a body would be partially or totally absorbed, reflected from its surface or transmitted through it. Identify the correct statement

B is the energy that is reflected by the body

B is the energy that is absorbed by the body

C is the energy that is absorbed by the body

D is the energy that is transmitted by the body

9. Which one is true regarding gases?

Transmissivity is zero

Absorptivity is zero

Reflectivity is zero

Reflectivity is unity

10. Let 220 W/m² of radiant energy is absorbed by a convex surface, 90 W/m² is reflected and 40 W/m² is transmitted through it. What is the value of absorptivity?

0.62

0.42

0.52

0.72